Wear- and oxidation-resisting hard alloys



United States Patent 3,368,889 WEAR- AND OXIDATION-RESISTING HARD ALLOYS Anton Biiumel, Goethestrasse 26, Lank (Lower Rhine), Germany N0 Drawing. Filed Nov. 4, 1064, Ser. No. 408,773 Claims priority, application Austria, Nov. 11, 1963, A 8,982/63 4 Claims. (Cl. 75-171) ABSTRACT OF THE DISCLOSURE This invention relates to an acid corrosion-resistant hard alloy consisting of 0.34.0% carbon, 15-40% chromium, up to 3.5% silicon, up to 2.0% manganese, 38- 80% cobalt with a combination of copper, molybdenum and nickel, 25-18% of at least one of the alloying elements from the class consisting of niobium, tantalum and vanadium, remainder iron and inevitable impurities, the cobalt content being at least 16%.

Weight loss, g./sq.

30% HNOa, room temp 30% HNOa,

boiling 1 Calculated as the balance.

The weight losses stated in the table for room temperature and boiling temperature in 30% nitric acid indicate a pronounced increase of the weight loss by tungsten (melt 3). Whereas a simultaneous addition of cobalt in melt 4 decreases the weight loss, however, the loW weight losses of the tungsten-free alloys 1 and 2 are not equaled. The most resistant alloys contain chromium and cobalt and no additional alloying elements.

Investigations of the corrosion behavior of carbides have shown that carbides of niobium, vanadium and tantalum have a high resistance to oxidation. This enables an increase of the wear resistance of the hard alloy by an addition of these elements, which are present in the hard alloy as carbides, without a reduction of the resistance to oxidizing media.

Tests carried out with hard alloys which contain niobium, vanadium and tantalum rather than tungsten have shown that the weight losses in boiling 30% nitric acid are in all cases below 1 gram per square meter-hour and average 0.5 gram per square meter-hour. Rockwell C hardness numbers between 53 and 61 were measured.

The composition range of the hard alloys which have been described hereinbefore and are stable in oxidizing media is defined as follows: 0.3-4.0% carbon, 15- 40% chromium, 0-3.5% silicon, 0-2.0% manganese, 38-80% cobalt, 25-18% niobium, tantalum or vanadium, individually or in combination, balance iron, more particularly 2.5% carbon, 28-30% chromium, 0.l5-0.45% silicon, 0.06-0.32% manganese, 45-60% cobalt, 25-18% niobium, tantalum or vanadium, balance iron. Silicon contents in excess of 1% have a favorable influence on the fluidity of the melt during welding.

It has also been found that the resistance of hard alloys containing cobalt, chromium and niobium; cobalt, chromium and tantalum; or cobalt, chromium and vanadium to corrosion in reducing acids can be increased by an addition of copper, molybdenum and nickel to the same values as with hard alloys containing cobalt, chromium and tungsten, provided that copper, molybdenum and nickel are added in combination. A content of 0.2-6% copper, 0.3-6% molybdenum and 0.5-10% nickel, with a corresponding reduction of the cobalt content, are effective and of technological interest. The hard alloys which contain niobium, tantalum or vanadium and corresponding additions have a high resistance to corrosion in reducing and oxidizing acids.

To confirm this statement, the weight losses in sulfuric and nitric acid will be stated for test alloys having the following compositions:

(1): Percent Carbon 1.84 Silicon 1.24 Manganese 0.2 Chromium 28.6 Niobium 5.0 Nickel 6.2 Molybdenum 3.55 Copper 1.5 Iron 2.6 Cobalt Balance Carbon 1.87 Silicon 1.10 Manganese 0.32 Chromium 29.5 Tantalum 4.72 Nickel 7.5 Molydenum 3.74 Copper 1.48 Iron 3.5 Cobalt Balance (3):

Carbon 1.98 Silicon 1.17 Manganese 0.17 Chromium 28.4 Vanadium 5.24 Nickel 7.8 Molybdenum 3.46 Copper 1.65 Iron 3.12 Cobalt Balance Weight Losses in Grams per Square M eter-II our Test Temperature Sulfuric Nitric Acid, percent Acid, percent The above weight loss data show that these types of alloys resist reducing as well as oxidizing acids. They are also superior to the comparable tungsten-containing alloys in wear resistance and when used for weld-surfacing are less liable to crack than the corresponding tungsten-containing alloys.

Hence, the invention provides corrosion-resisting hard alloys containing 0.3-4.0% carbon, 15-40% chromium, 03.5% silicon, 02.0% manganese, 38-80% cobalt, 2.5- 18% niobium, tantalum or vanadium, individually or in combination, preferably 0.7-2.5 carbon, 28-30% chromium, 0.150.45% silicon, 0.06O.32% manganese, cobalt, 25-18% niobium, tantalum or vanadium, balance iron, and optionally 0.26% copper, 0.36% molybdenum and 0.5-10% nickel to replace part of the cobalt.

What is claimed is:

1. An acid corrosion-resistant hard alloy consisting essentially of 0.3-4.0% carbon, 15-40% chromium, up to 35% silicon, up to 2.0% manganese, 38-80% cobalt and a combination of copper, molybdenum and nickel, 2.5- 18% of at least one of the alloying elements from the class consisting of niobium, tantalum and vanadium, balance iron and inevitable impurities, the cobalt content being at least 16%.

2. An acid corrosion-resisting hard alloy as set forth in claim 1, which consists essentially of 0.2-6% copper. 0.3-6% molybdenum and 05-10% nickel.

3. An acid corrosion resisting hard alloy as set forth in claim 1, which contains at least two of the alloying elements of the class consisting of niobium, tantalum and vanadium.

4. An acid corrosion-resisting hard alloy consisting essentially of 1.841.98% carbon, 1.101.24% silicon, 0.17- 0.32% manganese, 28.4-29.5% chromium, 4.72-5.24% niobium, 6.2-7.8% nickel, 3.463.74% molybdenum, 1.48-1.65% copper, 2.6-3.5% iron, balance cobalt and inevitable impurities.

References Cited UNITED STATES PATENTS 2,030,343 2/1936 Wissler -171 2,713,537 7/1955 Harris et al. 75-171 3,234,015 2/1966 Jones 75171 3,237,441 3/1966 Eberle 75171 FOREIGN PATENTS 515,049 7/1955 Canada.

DAVID L. RECK, Primary Examiner.

RICHARD O. DEAN, Examiner. 

